Context List

[Grundle]

Is it possible to make a list of contexts?  For example the following is a snippet of code (that obviously doesn't work) that i have written.

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(context 'ITEM)

(set 'title "")
(set 'link "")
(set 'content "")
(set 'item_date "")
(set 'author "")

(context 'MY_CONTEXT)

(set 'items '())

(define (create_item this_item)
(new ITEM 'MAIN:item-obj)
;;Item Title
(set 'item_obj:title "some title")
;;Item Author
(set 'item_obj:author "some author")
;;Item Date
(set 'item_obj:item_date "some date)
;;Item Body
(set 'item_obj:content "foo body")
;;Item Link/URL
(set 'item_obj:link "some URL")
(cons items item_obj)
)

;;Have some method here that calls create_items multiple times



That is a scaled down version (for brevity's sake).  Hopefully this gives a general idea of what I am trying to do.  Can anyone advise me on the best approach?

[Lutz]

This will give you a list of contexts:

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(filter context? (map eval (symbols 'MAIN)))


In your code you probably mean:

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(context 'MY_CONTEXT)

(set 'items '())

(define (create_item this_item)
   (new ITEM this_item)
   (set 'this_item (eval this_item))
   ;;Item Title
   (set 'this_item:title "some title")
   ;;Item Author
   (set 'this_item:author "some author")
   ;;Item Date
   (set 'this_item:item_date "some date")
   ;;Item Body
   (set 'this_item:content "foo body")
   ;;Item Link/URL
   (set 'this_item:link "some URL")
   (push this_tem items)
)
(context 'MAIN)

;; now you could do:

(MY_CONTEXT:create_item 'TEST-1)
(MY_CONTEXT:create_item 'TEST-2)

MY_CONTEXT:items => (TEST-2 TEST-1)

; from inside MY_CONTEXT you would do:

(create_item 'MAIN:TEST-1)
(create_item 'MAIN:TEST-1)

; because context symbols always belong to MAIN


This is the critical statement:



(set 'this_item (eval this_item))



Because you want to acces the context which is inside this_item but 'this_item' contains the symbol 'TEST-1 (which will contan the context TEST-1). So with 'eval' you have to peel off one layer.



In the last statment I use 'push', because 'cons' is non-destructive and would not change the list.



Lutz

[Grundle]

Thanks for the pointers, I found your explanation extremely helpful.  It turns out that the only thing I really needed to change was the following

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(cons items item_obj)


To this

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(push (eval item_obj) items)


I wasn't very specific about what "this_item" was and I noticed that you thought it was a context being passed, but it actually was a list of lists being passed.  Even so, your explanation of contexts and how they interact with each other answered a lot of questions for me.



Thanks!